Khan, Nazir; Bashir, Zahir; Price, Duncan M.; Liquid crystalline aromatic polyesters formed with terephthalic acid, phenyl hydroquinone, and naphthalene or anthracene. Journal of Applied Polymer Science 58(9) (1995) 1509-1516

The synthesis and characterisation of aromatic copolyesters containing terephthalic acid and phenylhydroquinone as the major constituents and either 1,4-naphthalenediol or 1,4-anthracenediol as the minority comonomer is described. Both polymers melted in the vicinity of 300C, giving birefringent fluids. Optical microscopy showed Schlieren textures consisting predominantly of inversion walls characteristic of the nematic phase. The clearing temperature was in the vicinity of 460C, but was accompanied by charring. DSC experiments showed a high glass transition temperature of 130-160C for both polymers. Crystal-nematic and nematic-isotropic endotherms were observed on heating; however, degradation took place near the isotropisation temp. Thus, on cooling, the sequence was reversible only if the previous heating was beyond the crystal-nematic but below the isotropisation temp. The polymers were stable in terms of gross wt. loss until about 450C, though there were indications that crosslinking occurred above about 400C over a short period of time. The polymers formed low-viscosity injection-moulding compounds, but to use them effectively, it would require mould-gate designs that reduce the "jetting" tendency for liquid crystal polymer melts, which result in weld lines.

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